This invention relates generally to techniques for generating pulses and more specifically to techniques for converting arbitrary analog waveforms to produce sequences of pulses.
Free running oscillations based on the relaxation oscillator approach are known. Many circuit configurations are possible. One example is a circuit comprising a tunnel diode connected in series with an inductor and a constant voltage source, to produce a periodic square waveform that has a constant frequency. U.S. Pat. No. 3,312,911 discloses a tunnel diode relaxation oscillator that produces a relaxation oscillation with the desired polarity. An op-amp based relaxation oscillator is described in U.S. Pat. No. 3,967,210. This oscillator is capable of producing oscillations in several selectable modes at different frequencies. All of these oscillators can be categorized as a free running oscillator.
The method and apparatus for a communication system disclosed in U.S. application Ser. No. 09/429,519 uses a controlled relaxation oscillator. In that application, the circuit is able to generate a number of desired oscillations followed by a substantially instant cessation of oscillatory behavior in response to an input waveform. Similarly, the circuit can also respond substantially instantly to yield a desired oscillatory behavior substantially without transients. However, the circuit disclosed in that application has reactive input impedance. The circuit is therefore frequency dependent which is not desirable under some conditions. In the U.S. application Ser. No. 09/805,845, a circuit is disclosed that has similar transfer function properties and which also possesses a resistive input impedance.
The approaches disclosed in the foregoing co-pending and co-owned application produce oscillatory behavior (i.e. generate groups of one or more pulses) when the operating point of the circuit is forced to the unstable region portion of the transfer characteristic. The oscillatory behavior ceases by forcing the operating point to a stable operating region portion of the transfer characteristic. However, the operating point of the disclosed circuits is determined solely by the input voltage. In some applications, it is desired to have the additional freedom to control the operating point via an additional input. As an example, an additional input that serves as an enable/disable control might be useful. Hence, there is a need for a circuit having transfer function characteristics that can be controlled dynamically.
In accordance with the present invention, producing pulses from analog waveforms includes providing a circuit having a transfer function characterized by having a stable operating region and an unstable operating region. The circuit is made to operate at a first operating point. The transfer function is adjusted by application of a signal to the circuit. In response, the circuit is made to operate at a second operating point. Either or both operating points can produce oscillatory behavior in the circuit. In one embodiment of the invention, the oscillatory behavior manifests itself as the production of groups of one or more pulses.
Further in accordance with the invention, producing information from an analog signal includes the foregoing to produce groups of one or more pulses. A decoding is made of the pulses to produce symbols representing the information.